About 480 residents were taking shelter at the Hachinohe Air Base, and 18 defense helicopters were mobilized for a damage assessment, Defense Minister Shinjiro Koizumi said.
About 200 passengers were stranded for the night at New Chitose Airport in Hokkaido, NHK reported.
The Japanese government was still assessing damages from the tsunami and late-evening quake, which struck at about 11:15 p.m. (1415 GMT) in the Pacific Ocean around 80 kilometers (50 miles) off the coast of Aomori, the northernmost prefecture of Japan's main Honshu island.
"I've never experienced such a big shaking," convenience store owner Nobuo Yamada told the public broadcaster NHK in the Aomori prefecture town of Hachinohe, adding that "luckily" power lines were still operating in his area.
A tsunami of 70 centimeters was measured in Kuji port in Iwate prefecture, just south of Aomori, and tsunami levels of up to 50 centimeters struck other coastal communities in the region, the Japan Meteorological Agency said
The Fire and Disaster Management Agency said 23 people were injured, including one seriously. Most of the victims were hit by falling objects, NHK reported, adding that several people were injured in a hotel in Hachinohe and a man in Tohoku was slightly hurt when his car fell into a hole.
The meteorological agency reported the quake's magnitude as 7.5, down from its earlier estimate of 7.6. It issued an alert for potential tsunami surges of up to 3 meters (10 feet) in some areas and later downgraded to an advisory.
The meteorological agency issued a caution about possible aftershocks in the coming days. It said there is a slight increase in risk of a magnitude 8-level quake and possible tsunami occurring along Japan's northeastern coast from Chiba, just east of Tokyo, to Hokkaido. The agency urged residents in 182 municipalities in the area to monitor their emergency preparedness in the coming week.
